Slit lamp having combination slit and lamp intensity control device

ABSTRACT

A slit lamp including a combination control device for simultaneously varying the width of a slit in an illumination column of the slit lamp and the intensity of a light beam from a lamp in the illumination column such that operation of the automatic control device automatically controls the intensity of the light beam in accordance with the width of the slit.

United States Patent McGrann et al.

[ Aug. 20, 1974 SLIT LAMP HAVING COMBINATION SLIT AND LAMP INTENSITY CONTROL DEVICE Inventors: John V. McGrann, Duxbury, Mass;

William M. Nalley, Silver Spring,

Assignee: Codman & Shurtletf, lnc., Randolf,

Mass.

Filed: June 25, 1973 Appl. N0.: 373,335

US. Cl. 351/14 Int. Cl A61!) 3/10 Field oi Search 351/14 [56] References Cited UNITED STATES PATENTS 3,535,027 l0/l970 Littmann et al. 35l/l4 Primary Examiner-Paul A. Sacher [5 7] ABSTRACT 14 Claims, 6 Drawing Figures Pmmgmuseoxsn 3% 3552 sum 3 (IF 3 SLIT LAMP HAVING COMBINATION SLIT AND LAMP INTENSITY CONTROL DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention pertains to slit lamps and, more particularly, to the control of slit width and lamp intensity in slit lamps.

2. Discussion of the Prior Art Slit lamps, which are conventionally utilized by ophthalmologists to examine the human eye, normally include a lamp for supplying a light beam through a slit, defined by movable blades, and various filters, pin holes and other optical components to a mirror for reflection into the eye of a patient while the opthalmologist or other operator utilizes a binocular microscope to focus on the eye. As the slit opening varies in area, the intensity of the lamp should be similarly varied in order to avoid discomfort to the patient when the slit is opened to its widest while providing sufficient light for eye examination when the slit opening is at its smallest.

In the past, slit lamps have utilized a rheostat con nected with a power transformer to permit the ophthalmologist to control lamp intensity, and a separate control has been provided to permit adjustment of the slit aperture. The requirement that the opthalmologist coordinate the operation of two independent controls is more than merely an inconvenience but requires the ophthalmologist to correlate slit opening to lamp intensity and, thus, represents a factor requiring the attention of the ophthalmologist thereby reducing his total concentration on the patient.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a combination slit and lamp control device for a slit lamp whereby an operator need only make a single adjustment to control both lamp intensity and the opening of the slit.

An additional object of the present invention is to construct a combination control device for a slit lamp which permits on-off control, selection of manual or automatic modes of operation; and, in the automatic mode of operation, permits the width of a slit to be changed while simultaneously, automatically altering lamp intensity.

A further object of the present invention is to provide a combination slit and lamp control device for a slit lamp wherein manipulation of a single knob can be utilized to simultaneously vary slit width and lamp intensity to automatically control light intensity in accordance with the width of the slit.

The present invention has another object in providing simple, reliable and inexpensive means for automatically adjusting lamp intensity and slit width simultaneously in a slit lamp while also providing a manual override for lamp intensity control.

Yet, an additional object of the present invention is to construct a combination control device for simultaneously controlling slit width and lamp intensity in a slit lamp such that the control device can be easily installed on conventional slit lamps.

A further object of the present invention isv to incorporate all of the electronic controls for a slit lamp in a single control device to obviate the need for separate control panels.

Some of the advantages of the present invention over .the prior art are that an operator utilizing the slit lamp can concentrate on a patient without having attention unduly diverted for control manipulations, the combination control device can be inexpensively manufactured, and the combination control device is designed to be operable with existing slit lamps thereby permitting modification of slit lamps in the field.

The present invention is generally characterized in a slit lamp including a lamp for providing a light beam, a slit mechanism for providing a slit of varying width, optical means for directing the light beam through the slit toward the eye of a patient, a circuit for variably supplying electrical power to the lamp to control the intensity of the light beam, and a control device for simultaneously operating the slit mechanism and the circuit to automatically control the intensity of the light beam in accordance with the width of the slit.

Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiment takne in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a slit lamp utilizing a combination slit and lamp control device according to the present invention.

FIGS. 2 and 3 are vertical sections of the illumination column of the slit lamp of FIG. 1.

FIG. 4 is a broken side elevation of the combination slit and lamp control device according to the present invention.

FIG. 5 is a section taken along line 5-5 of FIG. 4.

FIG. 6 is a schematic diagram of a control circuit for the slit lamp according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A slit lamp utilizing a combination slit and lamp control device according to the present invention is illustrated in FIG. I and includes a head rest frame 10 mounted on a table 12 or other suitable support with a chin support 14 extending between parallel uprights of the frame 10 and vertically adjustable to permit alignment of a patients eye level with an eye guide marker 16 on the head rest frame. A fixation light 18 depends from the top of the head rest frame and is adapted to be positioned such that examination of a patients eye is facilitated when the patient is looking at the fixation light. A carriage 20 is mounted to be movable along the table 12 relative to the head rest frame 10 by means of a spherical element, not shown, mounted in the carriage and riding on the surface of the table, the carriage 20 being slidable along a rod 22 carrying pinions 24 at its ends ridable on racks 26 formed in housings 28 mounted on the table. A control lever 30 extends from the carriage 20 to be moved by an operator to provide horizontal movement and fine focus of the slit lamp.

Mounted on the carriage 20 is a pivot assembly 32 including a hub 34 having an arm 36 extending transversely therefrom and cooperating with a vertical adjustment knob 38 for raising and lowering the pivot assembly. The pivot assembly 32 includes a microscope arm 40 carrying a binocular microscope body 42 and an illumination arm 44 carrying an illumination column 46, the arms 48 and 44 being pivotally mounted on a vertical pivot pin 48 supported by hub 34 such that the microscope body 42 and the illumination column 46 are pivotal about the same axis.

As best shown in FIGS. 2 and 3, the illumination column 46 includes a lamp 50 mounted in a housing 52 and arranged to direct a vertical beam of light through a condenser assembly 54 toward a first surface mirror 56 disposed at the bottom of the illumination column 46 on a post 57 in substantially horizontal, axial alignment with the microscope body 42 and oriented at substantially 45 to direct the light beam toward the eye of a patient. An inner cylindrical tube 58 carries an objective 60 at its lower end adjacent mirror 56, and an axially slidable sleeve 62 is disposed around tube 58 at the lower end, the sleeve 62 adapted to abut a shoulder formed by a collar 64 on the tube 58 mounting the objective 60. The illumination column 46 is supported on the illumination arm 44 by a pair of spaced columns 66 and 68 extending on opposite sides of mirror 56 between a combination control device 70 and a pair of ears 72 extending from collar 64, and the post 57 is similarly supported on the combination control device 70. Column 68 has a central bore therein for slidably receiving a control rod 74 having an end 76 abutting a flange 78 extending from sleeve 62, and a control rod 80 is slidably mounted along an outer tube 82 telescoping over tube 58, the control rod 80 having an end 84 abutting flange 78 and an end 86 extending within housing 52 and carrying a cam 88 movable with the control rod. A pair of blades 90 are pivotally mounted in housing 52 on pivot pins 92 below lamp 50, and each of the blades 90 carries a knife 94 forming a slit diaphragm and a cam follower roller 96 riding on a curved surface of cam 88.

The light beam provided by the lamp 50 and passing through the slit formed by blades 90 passes through an optical system including a filter assembly 98, an aperture assembly 100 and objective 60 to be deflected by mirror 56 toward the eye of a patient. The filter assembly 98 is operable by a lever 102 to selectively position one of a plurality of filters in the path of the light beam, such filters including a normal light filter, a heat absorption filter, a 50 percent density filter, a blue-green cobalt filter and any other desired filters. Similarly, the aperture assembly 100 is operated by a lever 104 to position an aperture of selected size in the pathof the light beam, such apertures desirably having sizes of 0.2 mm, 1 mm, 3 mm, 4 mm, 6 mm, 8 mm and 10 mm. A knob 106 is secured to tube 82 to permit the optical system to be rotated to vertically or horizontally orient the slit image.

With the exception of the combination control device 70, the above described structure of the slit lamp is conventional; and, thus, a detailed description thereof has been omitted. However, reference is made to the MENTOR Slit Lamp produced by Mentor Division of Codman & Shurtleff, Inc. and accompanying literature for more detailed structural and operational information relative to the above described structure.

The combination control device 70 is mounted on illumination arm 44 and, as shown in FIG. 4, includes a casing 108 on which columns 66 and 68 are mounted, the casing 108 having an aperture 110 in a top wall 112 thereof to permit control rod 74 to pass therethrough. Concentric inner and outer shafts 114 and 116 are rotatably mounted in casing 108 and extend through an end wall 118 of the casing, and a shaft 120 is rotatably mounted in suitable bearings and extends through an opposite end wall 122 of casing 108. A broached knob 124 is fixed to the external end of outer shaft 116, and a gear 126 is fixed to the outer shaft within the casing while shaft 120 similarly has a broached knob 128 fixed to its external end and is fixed to a gear 130 within the casing. A coupling shaft 132 carries gears 134 and 136 meshing with gears 126 and 130, respectively; and a cam 138 is fixed to shaft 132 to raise and lower rod 74 which has an end 140 riding on the cam surface, as best shown in FIG. 5. A preloading coupling shaft 142 has gears 144 and 146 meshing with gears 126 and 1130, respectively, and is mounted in parallel with coupling shaft 132 to remove backlash from the gear mechanism; and, since the couplings 132 and 142 positively mesh with the gears 126 and 130, rotation of either of knobs 124 or 128 causes rotation of the gear mechanism and the other knob such that the gear mechanism moves as a unit controllable from either end of the combination control device 70.

Disposed between the gears 126 and 130 is a control unit 148 formed of a manual control, 50 K9 potentiometer module 150, an automatic control, 50 K9 potentiometer module 152, a rotary on-off switch 154 and an automatic-manual, push-pull switch 156, switches 154 and 156 being controlled by inner shaft 114 which has a broached knob 158 fixed thereto adjacent knob 124. Potentiometer is operated by rotation of inner shaft 114 while the operation of potentiometer 152 is controlled by rotation of outer shaft 116. Rotation of inner shaft 114 also operates on-off switch 154, and the inner shaft 1 14 is axially slidable within the control unit 148 to operate push-pull switch 156. The control unit 148 can be formed of any desirable components, for example, the various Series 70 modules produced by Allen-Bradley Co., Milwaukee, Wis. With module packages as produced by the Allen-Bradley Co., the required 50 KO potentiometers and the rotary and pushpull switches can be selected as modules and assembled to be operable by inner and outer shafts; and, thus, the control unit 148 will not be discussed in further detail hereinafter. Reference is made to Publication 5,217, September 1971 of the Allen-Bradley Co. for further detail with respect to the modules of the control unit 148.

A control circuit 160 for the slit lamp according to the present invention is illustrated in FIG. 6 and includes a plug 161 adapted to be received in a receptacle provided with commercially available 115 v., 60 Hz electricity, the plug being connected across a primary winding of a transformer T through a fuse F and on-off switch 154, a capacitor C 1 being connected across the primary winding of transformer T. The secondary winding of transformer T has terminals 162 and 163 connected across the fixation light 18 and further connected across lamp 511 and a phase control circuit 164. The lamp 50 has one terminal connected to terminal 162 of the secondary winding of transformer T and the other terminal connected to a junction between a capacitor C2 and an inductor L forming an rf suppression circuit. The other terminal of capacitor C2 is connected to terminal 163 of the secondary winding of transformer T while the inductor L has its other terminal connected through an RC timing circuit 166, a hysteresis preventing circuit 168 and a bidirectional thyriston 170, such as a Triac, The RC timing circuit 166 includes a resistor R1 which is connected between inductor L and potentiometers 150 and 152 through ganged switches S1 and S2 of push-pull switch 156, respectively. The potentiometers 150 and 152 are connected through a capacitor C3 to the terminal 163 of the secondary winding of transformer T, and the junction of the capacitor C3 and potentiometers 150 and 152 is connected with a silicon bilateral switch SBS which is connected to the gate electrode of the Triac 170. The hysteresis prevention circuit 168 includes a resistor R3 connected in series with a diode D1 and a diode D2 connected between the bilaterial switch SBS and the junction of resistor R3 and diode D1.

The operation of the phase control circuit 164 will not be described in detail hereinafter other than with respect to the operation of push-pull switch 156 and potentiometers 150 and 152 since any conventional phase control circuit could be utilized with the present invention and since the operation of such circuits is well known. For more detail relative to the general operation of phase control circuit 164, reference is made to Motorola Application Note AN-526, 1970, published by Motorola Semi-Conductor Products, Inc.

In order to operate the slit lamp according to the present invention, the knob 158 is initially rotated to close on-off switch 154 and supply power to the fixation light 18 and the illumination lamp 50. If it is desired to manually control the intensity of the light beam from lamp 511 independent of the slit width, the knob 158 is pushed to axially move the inner shaft 114 and operate the push-pull switch 156 to place it in the manual mode. To this end, it is noted that switch S1 is normally open and switch S2 is normally closed such that once the knob 158 is depressed, switch S1 will be closed to connect potentiometer 150 in series with resistor R1 and capacitor C3 while removing potentiometer 152 from the circuit due to the opening of switch S2. With the combination control device 70 operated in the manual mode, rotation of knob 158 operates potentiometer 150 while rotation of either of knobs 124 or 128 controls the width of the slit formed between knives 94 on blades 90 such that in the manual mode of operation there is no inter-relationship between the width of the slit and the intensity of the light beam.

Rotation of either of knobs 124 or 128 causes rotation of coupling shaft 132 and cam 138 to operate the slit mechanism by controlling the raising and lowering of control rod 74 which, in turn, controls axial movement of sleeve 62 and corresponding movement of control rod 80. Thus, the cam 88 is moved up and down as the knobs 124 or 128 of the combination control device are turned, and the cam follower rollers 96 ride along the surface of the cam to pivot the blades 90 and vary the width of the slit formed between the knives 94. Rotation of knob 158 moves the tap along potentiometer 150; and, as the knob is turned clockwise, the intensity of the lamp is increased by decreasing the potentiometer resistance to decrease the charge time of capacitor C3 and corresponding breakdown of bilateral switch SBS to trigger Triac 170. That is, with each positive and negative cycle of the supply of electrical power, the point during the cycle at which the Triac 170 is triggered to energize the lamp 50 is controlled by the position of the potentiometer 150. Flicker of the lamp 50 is eliminated by the hysteresis prevention circuit 168 and rf emissions are suppressed by inductor L and capacitor C2.

To operate the slit lamp in the automatic mode, the knob 158 is merely rotated to operate switch 154 without pushing such that push-pull switch 156 remains in its normal state with switch S2 closed and switch S1 open thereby connecting potentiometer 152 in series with resistor R1 and capacitor C3. In the automatic mode of operation, movement of the knobs 124 and 128 along with controlling the size of the slit in the manner described above also controls the position of the tap of potentiometer 152'to control the intensity of the light beam provided by lamp 50 in a manner similar to that described above with respect to potentiometer 150. Accordingly, operation of a single knob, either knob 124 or knob 128, simultaneously controls the width of the slit and the intensity of the lamp 50 automatically thereby freeing the operator from adjusting light intensity to suit slit width.

At any time during the automatic mode of operation, the knob 158 can be depressed to operate the push-pull switch 156 and place the combination control device in the manual mode of operation thereby permitting control of the intensity of lamp 511 independent of slit width; and, similarly, any time during the manual mode of operation, the knob 158 can be pulled to return the combination control device to the automatic mode of operation. The tap of potentiometer 152 will be moved along with rotation of knobs 124 or 128 in both the manual and automatic modes of operation regardless of whether the potentiometer 152 is connected into the phase control circuit such that at any time the control device is placed in the automatic mode of operation, the potentiometer will be at a prescribed position relative to the slit width.

The relationship between light intensity and slit width is not necessarily linear; and, accordingly, the relationship between movement of the slit mechanism and changing of the time constant of the phase control circuit must be precisely correlated to provide appropriate slit width versus mean spherical candle power characteristics. Such correlation can be accomplished by calibrating the potentiometers or the mechanical linkage for changing slit width or both. For instance, by precisely selecting a configuration and dimensions for the cam 138 and the ratio of the gears 126, 130 to the gears 134, 136 the mechanical linkage can be calibrated for a standard potentiometer while the constant parameters of the timing components R1 and C3 in the phase control circuit are similarly calibrated for the standard potentiometer.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all subject matter described above or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A slit lamp comprising lamp means for providing a light beam;

slit means for providing a slit of varying width;

optical means for directing said light beam through said slit toward the eye of a patient;

circuit means for variably supplying electrical power to said lamp means to control the intensity of said light beam; and

control means for simultaneously operating said slit means and said circuit means to automatically control the intensity of said light beam in accordance with the widthof said slit.

2. A slit lamp as recited in claim 1 wherein said circuit means includes automatic resistance means variable to control the electrical power supplied to said lamp means and the intensity of said light beam, said slit means includes rod means movable to control the width of said slit, and said control means includes rotatable shaft means operable to vary said automatic resistance means and move said rod means simultaneously.

3. A slit lamp as recited in claim 2 wherein said shaft means includes a first shaft rotatable to control said resistance means, a second shaft rotatable to move said rod means and means rotatably coupling said first shaft with said second shaft.

4. A slit lamp as recited in claim 3 wherein said shaft means includes a third shaft concentric with and rotatable relative to said first shaft and further comprising on-off switch means operable in response to rotation of said third shaft and connected with said circuit means for controlling the supply of electrical power thereto.

5. A slit lamp as recited in claim 4 wherein said circuit means includes manual resistance means variable to control the electrical power supplied to said lamp means and the intensity of said light beam and further comprising manual-automatic switch means having an automatic state operably connecting said automatic resistance means in said circuit means and a manual state operably connecting said manual resistance means in said circuit means, said third shaft being rotatable to vary said manual resistance means and being axially movable to operate said manual-automatic switch means.

6. A slit lamp as recited in claim 5 and further comprising a casing having first and second end walls and housing said control means, said automatic resistance means, said manual resistance means, said on-off switch means and said manual-automatic switch means, said first and third shafts extending externally through said first end wall, said shaft means includes a fourth shaft extending through said second end wall and means rotatably coupling said fourth shaft with said second shaft such that said first, second and fourth shafts are rotatable together.

7. A slit lamp as recited in claim 6 wherein said means rotatably coupling said first shaft with said second shaft includes a first gear fixed to said first shaft and a second gear meshing with said first gear and fixed to said second shaft, said means rotatably coupling said fourth shaft with said second shaft includes a third gear fixed to said fourth shaft and spaced from said first gear and a fourth gear meshing with said third gear and fixed to said second shaft, and said automatic resistance means, said manual resistance means, said on-off switch means and said manual-automatic switch means are disposed in a modular control unit positioned between said first and third gears.

8. A slit lamp as recited in claim 7 and further comprising backlash preventing means housed in said casing including a coupling shaft having a pair of gears fixed thereto meshing with said first and third gears, respectively.

9. A slit lamp as recited in claim 8 and further comprising a pivoting assembly including a pivotal illumination arm mounting said casing and an illumination column mounted on said casing supporting said lamp means, said slit means and said optical means, said slit means including a cam rotatable with said second shaft to move said rod means and a pair of blades carrying knives defining said slit and movable relative to each other in response to movement of said rod means.

10. A slit lamp as recited in claim 1 and further comprising on-off switch means operable to control the supply of electrical power to said circuit means, said control means including shaft means for operating said on-off switch means.

11. A slit lamp as recited in claim 1 and further comprising switch means for disconnecting said control means from said circuit means to permit adjustment of the width of said slit without automatic adjustment of the intensity of said light beam.

12. A slit lamp as recited in claim 11 and further comprising on-off switch means operable to control the supply of electrical power to said circuit means, said control means including shaft means for operating said on-off switch means and said disconnecting switch means.

13. A slit lamp as recited in claim 1 wherein said circuit means includes automatic and manual resistance means each variable to control the electrical power supplied to said lamp means and the intensity of said light beam and further comprising manual-automatic switch means having an automatic state operably connecting said automatic resistance means in said circuit means and a manual state operably connecting said manual resistance means in said circuit means, said control means including shaft means for operating said manual-automatic switch means and for varying said automatic and variable resistance means.

14. A slit lamp as recited in claim 13 wherein said circuit means includes a phase control circuit and an rf suppression circuit connected in series with said lamp means. 

1. A slit lamp comprising lamp means for providing a light beam; slit means for providing a slit of varying width; optical means for directing said light beam through said slit toward the eye of a patient; circuit means for variably supplying electrical power to said lamp means to control the intensity of said light beam; and control means for simultaneously operating said slit means and said circuit means to automatically control the intensity of said light beam in accordance with the width of said slit.
 2. A slit lamp as recited in claim 1 wherein said circuit means includes automatic resistance means variable to control the electrical power supplied to said lamp means and the intensity of said light beam, said slit means includes rod means movable to control the width of said slit, and said control means includes rotatable shaft means operable to vary said automatic resistance means and move said rod means simultaneously.
 3. A slit lamp as recited in claim 2 wherein said shaft means includes a first shaft rotatable to control said resistance means, a second shaft rotatable to move said rod means and means rotatably coupling said first shaft with said second shaft.
 4. A slit lamp as recited in claim 3 wherein said shaft means includes a third shaft concentric with and rotatable relative to said first shaft and further comprising on-off switch means operable in response to rotation of said third shaft and connected with said circuit means for controlling the supply of electrical power thereto.
 5. A slit lamp as recited in claim 4 wherein said circuit means includes manual resistance means variable to control the electrical power supplied to said lamp means and the intensity of said light beam and further comprising manual-automatic switch means having an automatic state operably connecting said automatic resistance means in said circuit means and a manual state operably connecting said manual resistance means in said circuit means, said third shaft being rotatable to vary said manual resistance means and being axially movable to operate said manual-automatic switch means.
 6. A slit lamp as recited in claim 5 and further comprising a casing having first and second end walls and housing said control means, said automatic resistance means, said manual resistance means, said on-off switch means and said manual-automatic switch means, said first and third shafts extending externally through said first end wall, said shaft means includes a fourth shaft extending through said second end wall and means rotatably coupling said fourth shaft with said second shaft such that said first, second and fourth shafts are rotatable together.
 7. A slit lamp as recited in claim 6 wherein said means rotatably coupling said first shaft with said second shaft includes a first gear fixed to said first shaft and a second gear meshing with said first gear and fixed to said second shaft, said means rotatably coupling said fourth shaft with said second shaft includes a third gear fixed to said fourth shaft and spaced from said first gear and a fourth gear meshing with said third gear and fixed to said second shaft, and said automatic resistance means, said manual resistance means, said on-off switch meAns and said manual-automatic switch means are disposed in a modular control unit positioned between said first and third gears.
 8. A slit lamp as recited in claim 7 and further comprising backlash preventing means housed in said casing including a coupling shaft having a pair of gears fixed thereto meshing with said first and third gears, respectively.
 9. A slit lamp as recited in claim 8 and further comprising a pivoting assembly including a pivotal illumination arm mounting said casing and an illumination column mounted on said casing supporting said lamp means, said slit means and said optical means, said slit means including a cam rotatable with said second shaft to move said rod means and a pair of blades carrying knives defining said slit and movable relative to each other in response to movement of said rod means.
 10. A slit lamp as recited in claim 1 and further comprising on-off switch means operable to control the supply of electrical power to said circuit means, said control means including shaft means for operating said on-off switch means.
 11. A slit lamp as recited in claim 1 and further comprising switch means for disconnecting said control means from said circuit means to permit adjustment of the width of said slit without automatic adjustment of the intensity of said light beam.
 12. A slit lamp as recited in claim 11 and further comprising on-off switch means operable to control the supply of electrical power to said circuit means, said control means including shaft means for operating said on-off switch means and said disconnecting switch means.
 13. A slit lamp as recited in claim 1 wherein said circuit means includes automatic and manual resistance means each variable to control the electrical power supplied to said lamp means and the intensity of said light beam and further comprising manual-automatic switch means having an automatic state operably connecting said automatic resistance means in said circuit means and a manual state operably connecting said manual resistance means in said circuit means, said control means including shaft means for operating said manual-automatic switch means and for varying said automatic and variable resistance means.
 14. A slit lamp as recited in claim 13 wherein said circuit means includes a phase control circuit and an rf suppression circuit connected in series with said lamp means. 